High-voltage choked filament feed



June 10,1952. 7 w. H. BOSTICK 2,599,890

HIGH-VOLTAGE CHOKED FILAMENT FEED Filed Nov. 28, 1945 INVENTOR WINSTON H. BOSTICK ATTORNEY 'the application of such voltagexpulses.

these; voltage pulses may; attain; severalthousand volts in amplitude, it is clearthat-for proper operation av filament voltage source connected'in Patented June 10, 1952 Winston Bostick, West 'Medford; Mass, as-

-.signr,- by. mesne. assignments, :tor'theg Ilnited States; of, America represented. by. the; Secrotary of the-Navy Application Novernher 28; 1945;Serial N0; 631:4}8-

4: Claims.

, 1. 'Ihis invention relates to modulator circuits and more particula'rl'yto modulator circuits usingvery high modulation potential.

Radio frequency oscillators-often require-the continuous-circulation of current through an internal filament electrode. Certainof these oscillators: may require the additional applicationof a-modu1ating voltage to this same filament .electrode. Totake'an-example, ausual type of=mag netron oscillator-may contain a filament cathode structure; .various anode segments, and: an output coupling loop. It :iscommonpractice to provide directelectricalconnection between filament and cathode ofsuch an oscillator to avoid problems of highvoltage insulation. Methods of operat ingthis type of oscillator frequently. depend. on

grounding the anode and applyingmodulating voltages to its cathode. Sincethesemodulating voltages may take the. form. of very high ampli tude. voltage pulses, it will be .evident, from. the

foregoing considerations that: any filamentrvolt- .age source connected; directly to ;the oscillator filament .will-be subjected: tofandmust; withstand Since this manner must be. designed to have; proper electrical.protection against; such high Voltages even though its primary'iunction' is, one: of; supplying relatively low voltages to .operatethe oscillator'filament.

' Ifthe above mentioned. filament. volta e. source is, for example, a transformer itcanbe:seerrthat the high voltage: protection. requirement necessitates a type of transformer construction more complex than that for a conventional filament voltage transformer not designed to withstand high voltages. There are certain disadvantages arising from the necessityof using a high-voltageinsulated transformer, such as increased weight, size and cost. Connecting a transformer directly tothe oscillator filamentterminals also increases Y theircapacity to ground.

Itis an. object of this invention to-provide a modulator circuit which protects the; source of oscillator filament voltageagainst the modulating signals.

It is a further object of this invention to provide a means for utilizing a standard low-voltageinsulated filament transformer for oscillators which require application of high modulating voltages to their filaments.

It is a further object of this invention to provide a means for utilizing a standard low-voltfilament transformer.

age-insulated filament transformer-foramagnetron oscillators which: may undergo pulsed-aoperations;

It is. astill further object of this. invention toprovidemeansfor controlling the characteristics of a: modulating voltage signalappliedtathe filamenteofca radio frequency. oscillator,

It is .astill further object of this. invention to avoid. the distributed capacity to. ground .introduced by; connecting a' transformer directly-to the filamenti terminals of'a radio-frequencyoscillator.

These. and otherobjects-will become more .ap-

: parent. from theqfollowing description; o-f ..the:;1n-

wfilament l5..;-and cathode .l-Z: are shown connected together inyconventional'manner. The high voltage negativepulses applied to terminal l3 .are.ide-' rived from some external; source which-inthe instance shown determines thB'DOtQHtiSijOfIQImna1 l-3. accordingto. a rectansularvoltase envelope.

Two inductors I and- I11 are inserted-in series with the'filament leads. Inductor l6 isconnected between. one magnetron filament; terminalzand one terminal ofthesecondary winding 18;. Of. the filament transformer.- Inductor I1 is connected between the corresponding opposite magnetron filament terminal and the-correspondin -opposite terminal of the secondary windingl8tofi: the It will be evident.+.that these-twoinductors may be combinediain a single mechanical assembly to forma bi-filar choke as indicated in the drawing. Such'mechanicahconstruction, however, is not absolutely essentialto the operation of the invention, although this results in a compact arrangement which is generally desirable. In the operation of the invention the bifilar choke acts to prevent the high voltage negative pulses applied to the cathode of the magnetron from developing high voltages at the secondary of the filament transformer and yet said acter described may be considered to consist of the combination of numerous components of frequency high compared to the audio range. Thus it follows that the combination of the inductors I6 and I1 will offer a relatively high parallel im= pedance to the high voltage modulating pulses but a relatively low series impedance to the low frequency filament voltage.

As a result of the above action the filament transformer need not be designed to withstand such high voltage pulses. The consequent simplification in the design of the filament transformer yields certain definite advantages such as decreased size, weight, cost and lower effective capacity to ground. Furthermore, this invention permits grounding the filament transformer secondary winding l8 at any desired point. Capacitors 2| and 22 serve to bypass the secondary winding 18 in conventional manner.

It is known that the resultant shape of modulating pulses applied to a magnetron oscillator is definitely influenced by the impedance en countered by the pulses between their termina tion and ground. Some circuits have previously employed an inductor connected between the magnetron cathode and ground in parallel with the magnetron filament leads. The purpose of such an inductor was essentially to enable the unavoidable distributed capacitance of the circuit to ground to be discharged more rapidly at the end of the applied modulating pulse and thus improve or steepen the trailing edge of the pulse. Briefly, such an arrangement produced between the inductor and the distributed capacitance an oscillatory discharge, the start of which could be used to control the trailing edge of the applied pulse. The subsequent oscillation cycles may be Y damped out by known means. It should be noted that the parallel combination of the inductors l5 and ll of the embodiment may be used to accom plish these results.

A further possibility inherent in this inven-. tion is the utilization of the inductors l6 and I! to provide auxiliary voltage pulses which could be obtained by suitable coupling means to an external device from one or more points on either or both inductors I 6 and I1. Such pulses may be used for sampling, monitoring, triggering and other purposes.

The invention is to be limited only by the appended claims.

I claim:

'1. A pulse modulated ultra-high frequency magnetron transmitter circuit comprising a magnetron oscillator having electrically connected cathode and heater elements and a grounded anode, a heater power source, a coupling capacitor connected to said cathode for applying negative voltage pulses to modulate said oscillator, inductance elements included in a circuit shunting said magnetron to discharge the residual charge in said circuit at the termination of the transmitted pulse of high frequency oscillations, and heater leads connecting said heater to said source including said inductance elements.

2. A pulse modulated ultra-high frequency magnetron transmitter circuit comprising a magnetron oscillator having electrically connected cathode and heater elements and a grounded anode, a heater power source, heater leads connecting'said heater to said source, a coupling capacitor connected to said cathode for applying negative voltage pulses to modulate said magnetron oscillator, and inductance elements in a circuit shunting said magnetron to discharge the residual charge in said circuit at the termination of the transmitted pulse of high frequency oscillation, said inductance elements being included as a bifilar choke in said heater leads to isolate said heater power source from said voltage pulse.

3. A pulse modulation circuit for an ultra high frequency transmitter comprising, a magnetron oscillator having a grounded anode and electrically connected cathode and heater, a capacitor connected to said cathode to couple high voltage modulation pulses to said oscillator, a heater voltage transformer, leads connecting the transformer secondary winding to said heater, and a bifilar wound radio frequency choke in series with said heater leads, one of the paired inductors of said choke being in series with each lead, whereby high voltage modulation pulses are isolated from said transformer.

4. A pulse modulation circuit for an ultra high frequency transmitter comprising, a magnetron oscillator having a grounded anode and electrically connected cathode and heater, a capacitor 7 connected to said cathode to couple high voltage modulation pulses to said oscillator, a heater voltage transformer having separate primary and secondary windings, the secondary winding having a center tap connected to ground thereby dividing said winding into two halves, a capacitor shunting each half of said secondary winding, heater leads connecting the secondary Winding of said transformer to said heater, and a bifilar wound radio frequency choke in series with said heater leads, one of the paired inductors of said choke being in series with each lead, whereby high voltage modulation pulses are isolated from said transformer.

WINSTON H. BOSTICK.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,064,012 Kilgore Dec. 15, 1936 2,103,362 Hansell Dec. 28, 1937 2,416,718 Shockley Mar. 4, 1947 2,456,960 Lee et al Dec. 21, 1948 

